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Issue With Node Demands & Patterns

Hello there,

I have a model with five different types of demands with five associated patterns (domestic, commercial, municipal, apartments, and industrial). Each of these has it's own pattern created, the most complex being for domestic and apartments, where the factor varies throughout the entire day. (The other patterns only switch between 0 and 1 depending on the hour).

I am running my model in a max day scenario, and have calculated on my own what the sum of all demands should be at each hour, given the factor in my patterns that is shown for that hour. However, when running the model, the model gives me different numbers than I would expect. I've even looked at individual nodes to see what might be wrong.

For example, one node, Junction 2211, has Demand 1 (Domestic) set at 0.77 gpm. All other demands (2-5) are set at 0. The factor at Hour 1 for Demand 1's pattern is 0.33. Therefore, I would expect Junction 2211's demand at Hour 1 to be 0.25 gpm (0.77 * 0.33). However, the model is returning the number 0.16 gpm. I have no idea why this is.

Hopefully this outlines the problem well enough. Anyone have any thoughts/ideas on why this might be happening?

There could be several possibilities:Possibility 1 -Make sure you verify your Pattern timestep in the time settings matches your patterns. EG: if you have patterns with 24 values then your pattern timestep should be 1 hour. This will make sure the patterns used are as expected

​Possibility 2 - Check the pattern start value. If not "Zero" this will shift the pattern start and could change what is used when

Possibility 5- Make sure your patterns are "Normalized" If the values average to 1 then total demand will be exactly equal to the demand 1-10 values after the period is ended. If you add a global multiplier in the pattern value this also can make demands "higher" or lower than expected.

Possibility 6 - Are you getting a yellow light? If your accuracy is too high (above 0.01) or if it reaches max trials you may get an answer, but not a stable or "good" answer.

Possibility 7 - make sure your input units are as expected and output units are the same. Input units are set on the Simulation Options General Tab in the Flow and pressure units.
(click if need larger image)Simulation Option Units.PNG

I suspect this is caused by a global demand multiplier or a shift in the pattern from possibility 2 or 3 as the most likely cause.

Patrick Moore

Originally Posted by albrechtc

Hello there,

I have a model with five different types of demands with five associated patterns (domestic, commercial, municipal, apartments, and industrial). Each of these has it's own pattern created, the most complex being for domestic and apartments, where the factor varies throughout the entire day. (The other patterns only switch between 0 and 1 depending on the hour).

I am running my model in a max day scenario, and have calculated on my own what the sum of all demands should be at each hour, given the factor in my patterns that is shown for that hour. However, when running the model, the model gives me different numbers than I would expect. I've even looked at individual nodes to see what might be wrong.

For example, one node, Junction 2211, has Demand 1 (Domestic) set at 0.77 gpm. All other demands (2-5) are set at 0. The factor at Hour 1 for Demand 1's pattern is 0.33. Therefore, I would expect Junction 2211's demand at Hour 1 to be 0.25 gpm (0.77 * 0.33). However, the model is returning the number 0.16 gpm. I have no idea why this is.

Hopefully this outlines the problem well enough. Anyone have any thoughts/ideas on why this might be happening?

Thank you for your detailed response! I looked through all of the possibilities and I did end up changing the Pattern Start Value (Possibility 2). It was 1 and I changed it to "Zero". My patterns go from Hour 1 to Hour 24. When I run it with this pattern start value, at Hour "Zero" the demand at my example node - Junction 2211 is 0.25 gpm, which matches up with the demand pattern multipliers at Hour 1.
I am slightly confused as to the lining up of Hour Zero in the model and Hour 1 in the patterns. For Node 2211, as I said, at Hour Zero the model output demand = 0.25 gpm. This aligns with what I would expect to see using Hour 1 of the patterns. At Hour 1, the model output demand for that node = 0.19 gpm. This aligns with Hour 2 of the patterns.
Is this offset to be expected, between pattern time and model time? I think this confusion was why I originally has the Pattern start value in the model set to "1", but that created my original problem.

Most users Use Pattern Start at zero and Clock time Start at zero as this will always start at midnight and simulation hour zero will align with clock time zero. This will always use your first demand pattern in the first simulation period as well.

While adjusting the pattern start and clock time start may at times be advantageous, they can also easily lead to confusion for most modelers, so we generally only recommend adjusting these if you are an advanced user, as it is very easy to get yourself confused if you are not sure of what the model is doing with these two values.

These settings are directly out of EPANET (Our analysis engine) and if you feel you must adjust the clock time start and/or the Pattern Start values, make sure you only change one at a time and observe how this impacts the patterns and how they shift clearly before you change these values. Both can have an impact on when the patterns start and will impact what demands occur when in an EPS run.

Patrick Moore

Originally Posted by albrechtc

Hi Patrick,

Thank you for your detailed response! I looked through all of the possibilities and I did end up changing the Pattern Start Value (Possibility 2). It was 1 and I changed it to "Zero". My patterns go from Hour 1 to Hour 24. When I run it with this pattern start value, at Hour "Zero" the demand at my example node - Junction 2211 is 0.25 gpm, which matches up with the demand pattern multipliers at Hour 1.
I am slightly confused as to the lining up of Hour Zero in the model and Hour 1 in the patterns. For Node 2211, as I said, at Hour Zero the model output demand = 0.25 gpm. This aligns with what I would expect to see using Hour 1 of the patterns. At Hour 1, the model output demand for that node = 0.19 gpm. This aligns with Hour 2 of the patterns.
Is this offset to be expected, between pattern time and model time? I think this confusion was why I originally has the Pattern start value in the model set to "1", but that created my original problem.